This invention relates to the field of gasification of coal, and, specifically, provides a process for the combined devolatilization and gasification of coal or coal residues or mixtures of coal and petroleum residual oils. As available fuel sources become increasingly limited, and the price of fuel soars, the gasification of coal becomes an increasingly attractive and important process by which additional fuel sources may be liberated. Although much experimentation has been performed in this field, the developed processes suffer from a number of drawbacks or defects. Among the problems encountered are the relatively high cost of providing sufficient heat to achieve the high temperatures (above 2,000.degree. F.) necessary to achieve gasification, the low H.sub.2 :CO ratio for the synthesis gas product, the presence of tars and volatiles in the synthesis gas recovered, and the need to employ pure oxygen as an oxidizing medium.
The inventor has discovered that the need for high temperature and the use of pure oxygen can be avoided with resultant savings by an integrated coal devolatilization/gasification process such that the recycling of waste products can provide a heat carrier. The desired products can thereby be secured in large yields while the need for oxygen and the excessive loss of thermal energy are avoided.
U.S. patents describing prior art processes include U.S. Pat. Nos. 3,694,346, 3,702,516, 3,726,791 and 4,269,696. Each of these patents, and others in the field, requires the use of oxygen and encounters high thermal penalties which make the overall process far less efficient and less economically desirable.
Accordingly, it is one object of the present invention to provide a coal gasification process which avoids the need for the use of pure oxygen.
Another object of this invention is to provide a coal gasification process which enjoys a low thermal penalty by employing recycled and waste products as heat carriers.
A third object of this invention is the recovery of hydrogen rich volatiles and the preparation of a non-agglomerating char through coal devolatilization at an economically attractive cost.
A further object of this invention is to avoid the mixing of the products of coal devolatilization (tars, volatiles and pyrolysis off-gas) with the synthesis gas produced by char gasification in the riser-gasifier, thereby improving the efficiency and operability of subsequent heat recovery equipment on the synthesis gas product.
Another object of this invention is to minimize the carbon losses with the outgoing char, thereby maximizing gasification efficiency.